Nanoparticle composition and associated methods thereof

ABSTRACT

A nanoparticle composition is provided, wherein the composition comprises a nanoparticulate metal oxide; and a phosphorylated polyol comprising at least two phosphate groups. The polyol comprises one or more hydrophilic groups selected from the group consisting of polyethylene ether moieties, polypropylene ether moieties, polybutylene ether moieties, and combinations of two or more of the foregoing hydrophilic moieties. A method of making the nanoparticle composition is also provided. The nanoparticle compositions provided by the present invention may be used as contrast agents in medical imaging techniques such as X-ray and magnetic resonance imaging.

BACKGROUND

This invention relates generally to nanoparticle compositions which formstable aqueous suspensions, particularly nanoparticle compositions basedon transition metal oxides. Such nanoparticle compositions are usefulfor a variety of applications including diagnostic imaging.

Nanoparticles, i.e. particles whose diameters are appropriately measuredin nanometers, have been considered for a wide variety of end uses. Someof the uses require a substantial degree of hydrophilicity. However, ina number of instances, the material upon which nanoparticles are basedmay lack this attribute. For instance, nanoparticles with appropriateimaging properties for use as contrast agents for MR and/or X-rayimaging are typically based on transition metal oxides which lack thelevel of hydrophilicity required to form the stable aqueous suspensionsneeded for such applications. Therefore, efforts have been made tomodify the surface properties of such nanoparticles to be morecompatible with aqueous media and thereby enhance the stability ofaqueous suspensions of such nanoparticles. In some applications, it isalso desirable that the nanoparticles have a relatively monodisperseparticle size distribution. However, such surface treatments typicallyresult in a relatively polydisperse particle size distribution.

Typically, nanoparticle compositions in aqueous suspension are subjectto agglomeration and precipitation of the constituent nanoparticles.Surface treatments may be used to inhibit such agglomeration andprecipitation, and may take the form of adding one or more stabilizersubstances to a suspension of a nanoparticulate core species in adiluent. Such stabilizer substances are thought to attach to the surfaceof the suspended nanoparticulate core species and to form a barrier (orshell) interposed between at least a portion of the surface of thenanoparticulate core species and the diluent in which thenanoparticulate core species are suspended.

Formulations comprising nanoparticle compositions suitable for use inmedical imaging applications typically require purification prior topresentation to a subject. The various purification techniques employedmay degrade the hydrophilicity of the nanoparticle composition and mayalter the particle size distribution of the nanoparticle composition.Prudent medical practice and logic strongly suggest that formulationscontaining nanoparticle compositions to be used as contrast agents forin vivo use in human subjects will be subjected to rigorous purificationand be required to exhibit robust suspension stability in isotonicaqueous media, for example in 150 mM sodium chloride solution.

Thus, there is a need for nanoparticle compositions with improvedproperties, particularly related to increased hydrophilicity, stabilityin colloidal suspension, and enhanced safety.

BRIEF DESCRIPTION

In one embodiment the present invention provides a nanoparticlecomposition comprising a nanoparticulate metal oxide; and aphosphorylated polyol comprising at least two phosphate groups, whereinthe polyol comprises one or more hydrophilic groups selected from thegroup consisting of polyethylene ether moieties, polypropylene ethermoieties, polybutylene ether moieties, and combinations of two or moreof the foregoing hydrophilic moieties.

In another embodiment, the present invention provides a nanoparticlecomposition comprising a nanoparticulate iron oxide core; and a shellcomprising a phosphorylated polyol comprising at least two phosphategroups, wherein at least two of the phosphate groups occupy positions inthe phosphorylated polyol which constitute a 1, 2 or 1,3 spatialrelationship to one another and the polyol comprises a hydrophilic groupselected from the group consisting of polyethylene ether moieties,polypropylene ether moieties, polybutylene ether moieties, andcombinations of two or more of the foregoing hydrophilic moieties.

In yet another embodiment, the present invention provides a nanoparticlecomposition comprising a nanoparticulate metal oxide core, wherein themetal oxide comprises a metal selected from the group consisting ofiron, tantalum, zirconium, and hafnium; and a shell comprising aphosphorylated polyol comprising at least two phosphate groups, whereinat least two of the phosphate groups occupy positions in thephosphorylated polyol which constitute a 1, 2 or 1,3 spatialrelationship to one another and the polyol comprises a hydrophilic groupselected from the group consisting of polyethylene ether moieties,polypropylene ether moieties, polybutylene ether moieties, andcombinations of two or more of the foregoing hydrophilic moieties.

In yet another embodiment, the present invention provides a process formaking a nanoparticle composition comprising contacting ananoparticulate metal oxide core with a shell composition comprising aphosphorylated polyol comprising at least two phosphate groups and oneor more hydrophilic groups selected from the group consisting ofpolyethylene ether moieties, polypropylene ether moieties, polybutyleneether moieties, and combinations of two or more of the foregoinghydrophilic moieties.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is an idealized cross sectional view of a nanoparticle comprisinga core and a shell, in accordance with one embodiment of the presentinvention.

FIG. 2A is a T₁ weighted image (TE=4.1 ms) of a tumor in accordance withExample 29, before administration of iron oxide nanoparticlecomposition.

FIG. 2B is a T₁ weighted image (TE=4.1 ms) of a tumor in accordance withExample 29, 30 min after the administration of the nanoparticle contrastagent of Example 10.

FIG. 2C is a difference map of the differences between FIG. 2A and FIG.2B.

FIG. 2D is a T₂*-weighted image (TE=24.5 ms) of a tumor in accordancewith Example 29, before administration of iron oxide nanoparticlecomposition.

FIG. 2E is a T₂*-weighted image (TE=24.5 ms) of a tumor in accordancewith Example 29, 15 min after the administration of the nanoparticlecontrast agent of Example 10.

FIG. 2F is an R₂* relaxation difference map of the differences betweenFIG. 2D and FIG. 2E exhibiting a clear distinction between tumor andmuscle tissue.

DETAILED DESCRIPTION

In the following specification and the claims which follow, referencewill be made to a number of terms, which shall be defined to have thefollowing meanings.

The singular forms “a”, “an” and “the” include plural referents unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

As used herein, the term “solvent” can refer to a single solvent or amixture of solvents.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about”, is not to be limited to the precise valuespecified. In some instances, the approximating language may correspondto the precision of an instrument for measuring the value.

Unless specified otherwise, as used herein the term “phosphate group”refers to the bracketed group I shown below (and its ionized forms IIand III) and includes four constituent oxygen atoms and one constituentphosphorous atom but does not include the carbon atom shown. Thephosphate group is linked through one of its four oxygen atoms via abond (see dashed line) to a carbon atom in an organic moiety, thephosphate group and the organic moiety forming constituents of anorganic molecule, for example a phosphorylated polyol (See illustrativeexamples in the Experimental Section of this disclosure). Becausephosphate groups readily ionize to the corresponding mono anionic (Seegroup II) and dianionic (See group III) forms, the term phosphate groupas used herein includes each of these forms in addition to the fullyprotonated form featured in group I. The relative amounts of each of theforms I-III of a phosphate group present in, for example, aphosphorylated polyol, will depend on the environment in which thephosphate group is present. At high pH in aqueous media there should bemore of form III relative to form I, for example. In addition, for thepurposes of this disclosure, the term

phosphate group specifically excludes “polyphosphates” in which a firstphosphorous atom is linked to a second phosphorous atom via an oxygenatom without an intervening carbon atom. Structure IV below illustratesa polyphosphate as defined herein. As defined herein, a polyphosphatecomprises a first phosphorous atom (P¹) linked to a second phosphorousatom (P²) via an oxygen atom without an intervening carbon atom. In thepolyphosphate illustrated in structure IV the

polyphosphate group comprises seven oxygen atoms and two phosphorousatoms. An alternate illustrative polyphosphate group includes ten oxygenatoms and three phosphorous atoms. As illustrated in structure IV apolyphosphate group is linked to a moiety Q which may be an organicmoiety or an inorganic moiety. Polyphosphoric acid illustrates anexample of a polyphosphate in which Q is an inorganic moiety. TrisodiumO-methyl diphosphate illustrates an organic diphosphate wherein Q is amethyl group and the OH groups attached to phosphorous are ionized andattended by charge-balancing counterions (three sodium cations)(Chemical Papers 62 (2) 223-226 (2008)). Those of ordinary skill in theart will appreciate that as defined herein, the term polyphosphateencompasses both “acyclic polyphosphates” (wherein neither of the firstphosphorous atom (P¹) linked to the second phosphorous atom (P²) via anoxygen atom without an intervening carbon atom is part of a cyclicstructure) and “cyclic polyphosphates” (wherein in which at least one ofthe first phosphorous atom (P¹) linked to the second phosphorous atom(P²) via an oxygen atom without an intervening carbon atom is part of acyclic structure). Those of ordinary skill in the art will furtherappreciate that there are various ionized forms of polyphosphates andthat the term polyphosphate is meant to include the ionized forms of anidealized fully protonated polyphosphate, for example the fullyprotonated polyphosphate structure shown in structure IV above.

As discussed in detail below, embodiments of the present inventioninclude a nanoparticle composition comprising a nanoparticulate metaloxide, and a phosphorylated polyol, wherein the phosphorylated polyolcomprises at least two phosphate groups and a hydrophilic group, whereinthe phosphate groups are chemically and sterically accessible to themetal oxide and the hydrophilic group is selected from the groupconsisting of polyethylene ether moieties, polypropylene ether moieties,polybutylene ether moieties, and combinations of two or more of theforegoing hydrophilic moieties.

In various embodiments, the nanoparticle compositions provided by thepresent invention are sufficiently hydrophilic to form stable aqueouscolloidal suspensions that exhibit no substantial change in thehydrodynamic diameter (D_(H)) of constituent nanoparticles over aprolonged time frame (e.g. over several days to several weeks). A changein hydrodynamic diameter over time is a key indicator of colloidalsuspension stability. Thus, nanoparticle compositions that displayrobust stability in colloidal suspension should show little or noincrease in the hydrodynamic diameter (D_(H)) of the suspendedconstituent nanoparticles over the time period of interest. Hydrodynamicdiameter may be measured by dynamic light scattering (DLS). Those ofordinary skill in the art will understand that the term hydrodynamicdiameter (D_(H)) refers to the average hydrodynamic diameter.

As used herein, the term ‘nanoparticle composition’ refers to acomposition comprising constituent nanoparticles having average particlesize of less than 1 micrometer. As used herein, the term ‘size’ refersto the hydrodynamic diameter of the nanoparticles. In one embodiment,the nanoparticle composition provided by the present invention has aD_(H) in a of range from about 2 nm to about 500 nm. In an alternateembodiment, the nanoparticle composition provided by the presentinvention has a D_(H) in a range of from about 10 nm to 25 nm. In oneembodiment, the nanoparticle composition provided by the presentinvention has a D_(H) of less than 50 nm. In another embodiment, thenanoparticle composition provided by the present invention has a D_(H)of less than 10 nm. In yet another embodiment, the nanoparticlecomposition provided by the present invention has a D_(H) of less than 5nm. A small particle size may be advantageous in, for example,facilitating clearance of the nanoparticle composition from the kidneysand other organs of a subject following a medical imaging procedureemploying the nanoparticle composition as a contrast agent.

In one embodiment, the nanoparticle composition provided by the presentinvention comprises a core-shell structure, wherein the core comprises ananoparticulate metal oxide, and the shell comprises a phosphorylatedpolyol comprising at least two phosphate groups and one or morehydrophilic groups selected from the group consisting of polyethyleneether moieties, polypropylene ether moieties, polybutylene ethermoieties, and combinations of two or more of the foregoing hydrophilicmoieties.

In various embodiments, the shell comprising the phosphorylated polyolstabilizes the nanoparticulate metal oxide core and prevents theformation of larger metal oxide particles by association (agglomeration)of the nanoparticulate metal oxide core particles. One or moreembodiments of the invention are related to a nanoparticle compositionhaving the idealized core-shell structure shown in FIG. 1. Thenanoparticle composition 10 comprises a nanoparticulate metal oxide core12, and a shell 14 comprising a phosphorylated polyol as describedherein. In one embodiment, the present invention provides a nanoparticlecomposition characterized by its ability to form a stable aqueouscolloidal suspension that exhibits no substantial change in hydrodynamicdiameter (D_(H)) as determined by dynamic light scattering in 150 mMaqueous NaCl after tangential flow filtration and storage for one weekat room temperature.

The metal oxide core of the nanoparticle composition provided by thepresent invention has dimensions appropriately measured in nanometers.In various embodiments, the nanoparticulate metal oxide core may beprepared as a suspension in a diluent and the hydrodynamic diameter ofthe suspended nanoparticulate metal oxide core particles may bemeasured, for example by dynamic light scattering. In one embodiment,the nanoparticulate metal oxide core has a D_(H) as measured by dynamiclight scattering in a range from about 1 nm to about 30 nm. In analternate embodiment, the nanoparticulate metal oxide core has a D_(H)as measured by dynamic light scattering of about 5 nm. In one or moreembodiments, the nanoparticulate metal oxide core comprises ananoparticulate super paramagnetic iron oxide (SPIO) and has a D_(H) asmeasured by dynamic light scattering of less than about 25 nm.

The nanoparticulate metal oxide core typically comprises a transitionmetal oxide. In one embodiment, the nanoparticulate metal oxide coreconsists of a single transition metal oxide, for example tantalum oxidealone or iron oxide alone. In another embodiment, the nanoparticulatemetal oxide core comprises two or more transition metal oxides. Thus inone embodiment the nanoparticulate metal oxide core comprises bothtantalum oxide and hafnium oxide. In various embodiments, thenanoparticulate metal oxide core may comprise additional materials notconstituting metal oxides, such as metal nitrides and metal sulfides.Thus, in one embodiment the nanoparticulate metal oxide comprisestantalum oxide and hafnium nitride. In yet another embodiment, thenanoparticulate metal oxide core comprises tantalum oxide and tantalumsulfide.

In one embodiment, the nanoparticulate metal oxide core comprises atransition metal oxide selected from the group consisting of oxides oftungsten, tantalum, hafnium, zirconium, zinc, molybdenum, silver, iron,manganese, copper, cobalt, nickel and combinations of two or more of theforegoing transition metal oxides. In one specific embodiment, thetransition metal oxide is tantalum oxide. In an alternate embodiment,the transition metal oxide is iron oxide. Typically, the nanoparticulatemetal oxide core comprises at least 30% by weight of the transitionmetal component of the transition metal oxide. In one embodiment, thenanoparticulate metal oxide core comprises at least 50% by weight of thetransition metal component. In yet another embodiment, thenanoparticulate metal oxide core comprises at least 75% by weight of thetransition metal component. Those of ordinary skill in the art willappreciate that a relatively high transition metal content in thenanoparticulate metal oxide core can provide nanoparticle compositionswith a relatively higher degree of radiopacity per unit volume, therebyimparting more efficient performance as a contrast agent.

For use as X-ray contrast agents, the nanoparticle composition providedby the present invention should be substantially more radiopaque thanthe tissue and bone matter typically found in living organisms. Incertain embodiments, the present invention provides nanoparticlecompositions comprising nanoparticulate metal oxide cores comprisingmetal atoms having an atomic number greater than or equal to 34. Suchnanoparticle compositions may be effective as imaging agents whenpresented to a subject in a medical imaging formulation having ananoparticle composition concentration sufficient to provide aneffective metal concentration in the subject's blood during the imagingprocedure of approximately 50 mM. Such materials are likely yieldappropriate contrast enhancement of about 30 Hounsfield units (HU) orgreater. Of special interest are materials that lead to a contrastenhancement in a range from about 100 Hounsfield to about 5000Hounsfield units. Examples of transition metal elements that may providethis property include tungsten, tantalum, hafnium, zirconium,molybdenum, silver, and zinc. In one embodiment, the present inventionprovides a nanoparticle composition suitable for use in X-ray imagingapplications such as computed tomography (CT), the nanoparticlecomposition comprising a nanoparticulate metal oxide core comprisingtantalum oxide.

In one or more embodiments, the core of the nanoparticle compositioncomprises tantalum oxide with a particle size up to about 6 nm. Suchembodiments may be particularly attractive in imaging techniques thatapply X-rays to generate imaging data, due to the high degree ofradiopacity of the tantalum-containing core and the small size that aidsrapid renal clearance, for example.

In some embodiments, the metal oxide core comprises a transition metal,which exhibits magnetic behavior, including, for example,superparamagnetic behavior. In some embodiments, the metal oxide corecomprises a paramagnetic metal, selected from the group consisting ofiron, manganese, copper, cobalt, nickel, and combinations thereof. In aspecific embodiment, the metal oxide core comprises superparamagneticiron oxide (SPIO). In one embodiment, the iron oxide is doped withanother metal.

In some embodiments, the nanoparticle compositions of the presentinvention may be used as magnetic resonance (MR) contrast agents. Foruse as MR contrast agents the nanoparticle composition provided by thepresent invention advantageously comprises a paramagnetic metal species,with those compositions that comprise a superparamagnetic metal speciesbeing of particular interest. Examples of potential paramagnetic andsuperparamagnetic materials include materials comprising one or more ofiron, manganese, copper, cobalt, nickel or zinc. A particularlyinteresting group of materials are those based upon iron oxide,especially SPIO's, which typically comprise from about 65% to about 75%iron by weight. In one embodiment, the nanoparticulate metal oxide corecomprises a iron compound having general formula [Fe₂ ⁺O₃]_(x)[Fe₂⁺O₃(M²⁺O)]_(1-x) wherein 1≧x≧0 and M²⁺ is a metal cation such as cationsof iron, manganese, nickel, cobalt, magnesium, copper, zinc and acombination of such cations. Examples of iron compounds falling withinthe scope of this general formula include magnetite (Fe₃O₄) when themetal cation (M²⁺) is ferrous ion (Fe²⁺) and x=0; and maghemite(γ-Fe₂O₃) when x=1.

As shown in the idealized structure shown in FIG. 1, the nanoparticlecomposition may comprise a shell which completely covers thenanoparticulate metal oxide core. Thus, in certain embodiments, thenanoparticle composition is said to comprise a shell which substantiallycovers the core. As used herein, the term “substantially covers” meansthat a percentage surface coverage of the core by the shell is greaterthan about 20%. As used herein, the term percentage surface coveragerefers to the ratio of the core surface covered by the shell to the coresurface not covered by the shell. In some embodiments, the percentagesurface coverage of the nanoparticle may be greater than about 40%.

In some embodiments, the shell may facilitate improved water solubility,reduce aggregate formation, prevent oxidation of nanoparticles, maintainthe uniformity of the core-shell entity, and/or provide biocompatibilityfor the nanoparticle compositions.

The average thickness of shell is typically in a range from about 1 toabout 50 nm. In one embodiment, the shell has an average thickness lessthan 50 nm. In another embodiment, the shell has an average thickness ofless than 8 nm. In yet another embodiment, the shell has an averagethickness of less than 5 nm.

The nanoparticle compositions provided by the present invention maycomprise more than one shell layer disposed on the nanoparticulate metaloxide core. By judicious selection of processing conditions, ananoparticulate metal oxide core species may be prepared as a suspensionin a diluent and thereafter treated under a first set of conditions withone or more stabilizer substances to generate a first nanoparticlecomposition comprising a first shell, and thereafter the firstnanoparticle composition is treated under a second set of conditionswith one or more different stabilizer substances which generate a secondnanoparticle composition comprising both the first shell and a secondshell. In embodiments comprising a plurality of shells, at least one ofthe shells comprises a phosphorylated polyol comprising at least twophosphate groups and one or more hydrophilic groups selected from thegroup consisting of polyethylene ether moieties, polypropylene ethermoieties, polybutylene ether moieties, and combinations of two or moreof the foregoing hydrophilic moieties. In one embodiment, a single shellmay cover essentially the entire surface of the nanoparticulate metaloxide core. In another embodiment, the present invention provides ananoparticle composition comprising a single nanoparticulate metal oxidecore composition and multiple shell compositions, as in the case where ananoparticulate metal oxide core species is prepared as a suspension ina diluent, the suspension is divided in half and each half is treatedwith a different phosphorylated polyol, and subsequently the halves arerecombined. Thus, within a nanoparticle composition provided by thepresent invention, individual particles may comprise shells which areessentially identical to the shells of companion particles within thenanoparticle composition; or the shells of constituent particles withinthe nanoparticle composition may differ from one another in composition.

As noted, the nanoparticle compositions provided by the presentinvention comprise a phosphorylated polyol, the phosphorylated polyolcomprising at least two phosphate groups and one or more hydrophilicgroups. The hydrophilic group (or groups) is selected from the groupconsisting of polyethylene ether moieties, polypropylene ether moieties,polybutylene ether moieties, and combinations of two or more of theforegoing hydrophilic moieties. Polyethylene ether moieties are definedas moieties comprising oxyethyleneoxy structural units —OCH₂CH₂O—,and/or substituted oxyethyleneoxy structural units. For convenience andbecause of the close structural association with the term polyethyleneglycol (PEG), such moieties may at times herein be referred to as PEGgroups, or PEG moieties, and are characterized by a moiety molecularweight. Illustrative polyethylene ether moieties are given in Table 1below and throughout this disclosure. Similarly, polypropylene ethermoieties are defined as moieties comprising oxypropyleneoxy structuralunits —OCH₂CH₂CH₂O— and/or substituted oxypropyleneoxy structural units.For convenience polypropylene ether moieties may at times herein bereferred to as polypropylene glycol groups or moieties. Similarly,polybutylene ether moieties are defined as moieties comprisingoxybutyleneoxy structural units —OCH₂CH₂CH₂CH₂O— and/or substitutedoxybutyleneoxy structural units. For convenience polybuylene ethermoieties may at times herein be referred to as poly-THF moieties.

Illustrative phosphorylated polyols used in, and provided by the presentinvention are given in Table 1 below. In each of Entries 1a-1f, theillustrated phosphorylated polyol comprises at least two phosphategroups and one or more hydrophilic groups selected from the groupconsisting of one or more of a polyethylene ether moieties,polypropylene ether moieties, polybutylene ether moieties, andcombinations of two or more of the foregoing hydrophilic moieties.

TABLE 1 Exemplary Phosphorylated Polyols and Constituent StructuralElements Entry Structure of Phosphorylated Polyol 1a

1b

1c

1d

1e

1f

As will be appreciated by those of ordinary skill in the art thephosphate groups present in the phosphorylated polyol may be configuredsuch that two phosphate groups within the same phosphorylated polyoloccupy positions which constitute a 1,2; 1,3; 1,4; 1,5; or 1,6 spatialrelationship to one another. In Table 1 Example 1a illustrates aphosphorylated polyol in which two phosphate groups are configured in a1,3 spatial relationship with respect to each other. Example 1billustrates a phosphorylated polyol in which two phosphate groups areconfigured in a 1,2 spatial relationship with respect to each other.Those of ordinary skill in the art will be familiar with suchdistinctions. A 1,2 spatial relationship of the at least two phosphategroups includes embodiments which are 1,2-bisphosphates;2,3-bisphosphates; 3,4-bisphosphates; 4,5-bisphosphates,5,6-bisphosphates and so on. A 1,3 spatial relationship of the at leasttwo phosphate groups includes embodiments which are 1,3-bisphosphates;2,4-bisphosphates; 3,5-bisphosphates; 4,6-bisphosphates;5,7-bisphosphates and so on. Those of ordinary skill in the art willfully understand the extension of this principle to 1,4; 1,5; and 1,6spatial relationships of the at least two phosphate groups.

As noted, the phosphorylated polyol comprises one or more hydrophilicgroups selected from the group consisting of polyethylene ethermoieties, polypropylene ether moieties, polybutylene ether moieties, andcombinations of two or more of the foregoing hydrophilic moieties. Theeffectiveness of the phosphorylated polyol in stabilizing thenanoparticulate metal oxide core (and the nanoparticle composition as awhole) has been found to depend upon its structure. In variousembodiments, the effectiveness of the phosphorylated polyol instabilizing the nanoparticulate metal oxide core is dependent upon thesize of the hydrophilic moiety which may at times herein be described interms of the group molecular weight of the hydrophilic group. Ingeneral, the structure of the phosphorylated polyol may be tailored tobe effective in stabilizing a particular nanoparticulate metal oxidecore, and the hydrophilic group present in the phosphorylated polyol mayhave either a relatively low group molecular weight (e.g. less than 100grams per “mole”) or a relatively high group molecular weight (e.g. morethan 10,000 grams per “mole”). Those of ordinary skill in the art willunderstand that because the hydrophilic group comprises one or more of apolyethylene ether moiety, a polypropylene ether moiety, a polybutyleneether moiety, and combinations of two or more of the foregoinghydrophilic moieties, the size and molecular weights of these moieties,at times herein referred to as moiety molecular weight, will contributeto the group molecular weight of the hydrophilic group as a whole. Inone embodiment, the hydrophilic group comprises a polyethylene ethermoiety having a moiety molecular weight in a range from about 750daltons to about 20,000 daltons. In an alternate embodiment, thehydrophilic group comprises a polyethylene ether moiety having a moietymolecular weight of about 2000 daltons. In yet another embodiment, thehydrophilic group comprises a polyethylene ether moiety having a moietymolecular weight of less than 20,000 daltons. In yet still anotherembodiment, the hydrophilic group comprises a polyethylene ether moietyhaving a moiety molecular weight of less than 2000 daltons. In yetanother embodiment, the hydrophilic group comprises a polyethylene ethermoiety having a moiety molecular weight of less than 350 daltons. Asused herein, “daltons” and “grams per mole” may be used asinterchangeable terms which when applied either to the group molecularweight of a hydrophilic group or the moiety molecular weight of apolyethylene ether moiety, polypropylene ether moiety, polybutyleneether moiety, combinations of two or more of the foregoing hydrophilicmoieties, and substituted variants of such moieties, and expresses theweight in grams of the that group or moiety present in a mole of thephosphorylated polyol which contains it.

The intended end use of the nanoparticle composition may impact theselection of the hydrophilic groups used in the phosphorylated polyol.For instance, where the nanoparticle compositions are to be used invivo, particularly in human subjects, it may be desirable to avoidhydrophilic groups containing ionic groups which might bind strongly totissue components such as proteins. For in vivo use, hydrophilic groupswith essentially no net charge, such as polyalkylene ethers are ofparticular interest. In addition, for use in human subjects, hydrophilicgroups that are innocuous and permit the nanoparticle composition to beeasily and reproducibly characterized for safety evaluation areparticularly desirable. The nanoparticle composition provided by thepresent invention typically has a zeta potential in a range from about−40 mV and +40 mV.

In one embodiment, the phosphorylated polyol has structure V

wherein n is an integer from about 6 to about 150 and R¹ is an alkylgroup or a hydrogen atom. The phosphorylated 1,2-diol V is illustratedby phosphorylated polyol 10 (Experimental Section Example 5, n=10,R¹=methyl) also referred to herein as 1,2BPP440. Phosphorylated 1,2-diolV is further illustrated by phosphorylated polyol 15 (ExperimentalSection Example 7, n=17, R¹=methyl) also referred to herein as1,2BPP750. In one embodiment, the present invention a phosphorylated1,2-diol having structure V wherein n is in a range from about 16 toabout 150 and R¹ is an alkyl group or a hydrogen atom. See, for example,phosphorylated 1,2-diol 20 ((Experimental Section Example 9, n=44,R¹=methyl).

In an alternate embodiment, the phosphorylated polyol has structure VI

wherein n is an integer from about 6 to about 150 and R¹ is an alkylgroup or a hydrogen atom. The phosphorylated 1,3-diol VI is illustratedby phosphorylated polyol 27 (Experimental Section Example 13, n=7,R¹=methyl) also referred to herein as 1,3BPP350. In one embodiment, thepresent invention a phosphorylated 1,3-diol having structure VI whereinn is in a range from about 16 to about 150 and R¹ is an alkyl group or ahydrogen atom. See, for example, phosphorylated 1,3-diol 31((Experimental Section Example 15, n=44, R¹=methyl) also referred toherein as 1,3BPP2000.

In yet another embodiment, the phosphorylated polyol comprising at leasttwo phosphate groups and one or more hydrophilic groups has structureXVIII

wherein O—R² is independently at each occurrence a phosphate group, ahydroxy group, or a polyethylene ether moiety.

As used herein in relation to phosphorylated polyols and nanoparticlecompositions comprising such phosphorylated polyols or nanoparticlecompositions comprising structural units derived from suchphosphorylated polyols, the designation “1,2-BPP350” refers to aphosphorylated polyol comprising two phosphate groups configured in a1,2 spatial relationship and a polyethylene ether moiety having a moietymolecular weight of 350 daltons. Similarly, the designation “1,2-BPP440”refers to a phosphorylated polyol comprising two phosphate groupsconfigured in a 1,2 spatial relationship and a polyethylene ether moietyhaving moiety molecular weight of 440 daltons.

As used herein the designation P2P4Man refers to a phosphorylatedmannitol comprising approximately two phosphate groups per mannitolresidue and approximately four hydrophilic groups comprisingpolyethylene ether moieties. Structure 23 in the Experimental Sectionillustrates such a mannitol-based phosphorylated polyol.

Nanoparticle compositions provided by the present invention areillustrated by structures VII-XVI below wherein the disc-shapedcomponent labeled Fe₃O₄ represents a nanoparticulate metal oxide coreand the associated phosphorylated polyol structure represents one ormore phosphorylated polyols bound to the nanoparticulate metal oxidecore. Structures VII-XVI are not meant to suggest a 1:1 stoichiometrybetween the nanoparticulate metal oxide core and the phosphorylatedpolyol, but rather to identify the nanoparticle composition ascomprising a the nanoparticulate metal oxide care and at least onephosphorylated polyol. As noted, the phosphorylated polyol may be in afully protonated form as shown in structures VII-XVI, or in an ionizedform. (See Forms II and III herein). Typically, a plurality ofphosphorylated polyols will be associated with the surface of a givennanoparticulate metal oxide core particle. In some embodiments, thephosphorylated polyol is bound to the nanoparticulate metal oxide corevia hydrogen bonds. In some embodiments, the phosphorylated polyol isbound to the nanoparticulate metal oxide core via at least one covalentbond. In other embodiments, the phosphorylated polyol may be bound tothe nanoparticulate metal oxide core via ionic bonds. In certainembodiments, the precise nature of the chemistry through which thephosphorylated polyol is bound to the nanoparticulate metal oxide coremay not be well understood. Notwithstanding such uncertainty, basicstructure-activity principles for a variety of such nanoparticlecompositions provided by the present invention may be discerned throughexperimentation, and such experimentally determined structure-activityprinciples are disclosed herein.

As illustrated in structures XI, XII, XIII and XIV the phosphorylatedpolyol component of the nanoparticle composition may, in certainembodiments, comprise a hydrophilic group containing groups in additionto the ether linkages (—O—) found in polyalkylene ether moieties. Thus,a wide variety of functional groups in addition to ether groups may bepresent in the phosphorylated polyol, for example ester groups, aminegroups, amide groups, carbamate groups, urea groups, carbonate groups,thioether groups, selenoether groups, siloxane groups, sulfinyl groups,sulfonyl groups, and combinations of two or more of the foregoinggroups. As will be appreciated by those of ordinary skill in the art,such functional groups may be constituents of the hydrophilic groupitself or may constitute a part of the phosphorylated polyol which isnot identified as the hydrophilic group. The intended end use of thenanoparticle compositions may impact the choice of such functionalgroups.

As noted, the nanoparticle composition provided by the present inventiontypically comprises a transition metal oxide core and a shell comprisedof a phosphorylated polyol. In the product nanoparticle composition theratio of the shell to the core may be determined by elemental analysis.From knowledge of the chemical make up of the metal oxide nanoparticlesand their average size before treatment with the phosphorylated polyol,a calculation can be made of the amount of phosphorylated polyol pernanoparticulate metal oxide core particle. In one embodiment, thepresent invention provides a nanoparticle composition comprising ananoparticulate iron oxide core and a phosphorylated polyol shellwherein the molar ratio of phosphorylated polyol to iron is in a rangefrom about 0.01 to about 0.25. In an alternate embodiment, the presentinvention provides a nanoparticle composition comprising ananoparticulate tantalum oxide core and a phosphorylated polyol shellwherein the molar ratio of phosphorylated polyol to tantalum is in arange from about 1 to about 2. In one embodiment, the present inventionprovides a nanoparticle composition comprising a nanoparticulate SPIOcore, and a phosphorylated polyol shell wherein the molar ratio of thephosphorylated polyol to the iron in the nanoparticulate SPIO core is ina range from about 0.01 to 0.25.

One aspect of the invention relates to methods for making thenanoparticle compositions. In general, the method for making ananoparticle composition comprises contacting a nanoparticulate metaloxide core with a phosphorylated polyol shell composition of the presentinvention. The Experimental Section of this disclosure providesextensive guidance on the preparation of the nanoparticle compositionprovided by the present invention. Typically, the contacting is carriedout in a mixture comprising at least one organic solvent and water.

In one embodiment, the method comprises providing a nanoparticulatemetal oxide core, and disposing a phosphorylated polyol shell on thecore. In one or more embodiments, the step of providing ananoparticulate metal oxide core comprises providing a first precursormaterial comprising a transition metal, the first precursor materialbeing susceptible to nanoparticulate metal oxide formation. In oneembodiment, the first precursor material may react with an organic acidto generate the nanoparticulate metal oxide core. The term “reacts”includes mixing two or more reactants under conditions which allow themto interact. In an alternate embodiment, the first precursor materialmay decompose to generate the nanoparticulate metal oxide core. Inanother embodiment, the first precursor material may hydrolyze togenerate the nanoparticulate metal oxide core. Thus, in one embodimentnanoparticulate metal oxide core is provided by hydrolysis of a metalalkoxide in the presence of an organic acid. For example,nanoparticulate tantalum oxide tantalum may be prepared by hydrolysis oftantalum ethoxide. The organic acid may be, for instance, a carboxylicacid such as isobutyric acid. The hydrolysis reaction may be carried outin the presence of an alcohol solvent, such as 1-propanol or methanol.Methods for the preparation of nanoparticulate metal oxide particles arewell known in the art and any suitable method for making a nanoparticlecore of an appropriate material may be suitable for use in this method.

The Experimental Section of this disclosure provides detailed guidanceon protocols for disposing a phosphorylated polyol shell on thenanoparticulate metal oxide core. In one or more embodiments, disposingthe shell on the core comprises providing a second precursor materialcomprising a phosphorylated polyol or a precursor thereto. In someembodiments, the precursor to the phosphorylated polyol may undergo ahydrolysis reaction in the presence of the nanoparticulate metal oxidecore and thereafter attach to the surface of the nanoparticulate metaloxide core. In an alternate embodiment, the precursor to thephosphorylated polyol can be attached to the surface of thenanoparticulate metal oxide core and thereafter hydrolyzed.

As noted, the nanoparticle compositions provided by the presentinvention may be used as contrast agents for diagnostic imaging. In suchan application, these nanoparticle compositions are administered to asubject, in some embodiments a mammalian subject, and then the subjectis thereafter subjected to imaging. The nanoparticle compositionsprovided by the present invention may be particularly useful in MR andX-ray imaging though they may also find utility as contrast agents inultrasound or radioactive tracer imaging. In addition, the nanoparticlecompositions provided by the present invention may be useful in otherareas such as cell culture infusion.

In one embodiment, the present invention provides a diagnostic agentcomposition suitable for injection into a mammalian subject, and thediagnostic agent composition comprises a nanoparticle composition and apharmaceutically acceptable carrier or excipient. The nanoparticlecomposition comprises a nanoparticulate metal oxide and a phosphorylatedpolyol, the phosphorylated polyol comprising at least two phosphategroups and one or more hydrophilic groups selected from the groupconsisting of polyethylene ether moieties, polypropylene ether moieties,polybutylene ether moieties, and combinations of two or more of theforegoing hydrophilic moieties. In one embodiment, the excipient is anoptional component of the diagnostic agent composition. Suitableexcipients are illustrated by, but not limited to, one or more of salts,disintegrators, binders, fillers, and lubricants. In one embodiment, thepharmaceutically acceptable carrier may be substantially water.

Diagnostic agent compositions provided by the present invention may beprepared by contacting a nanoparticle composition of the presentinvention with a pharmaceutically acceptable carrier and/or excipient.

In yet another embodiment, the present invention provides a method ofperforming diagnostic imaging, the method comprising (a) administering adiagnostic agent composition of the present invention to a subject in apharmaceutically acceptable carrier or excipient; and (b) subjecting thesubject to diagnostic imaging, wherein the diagnostic agent compositionacts as a contrast agent. The diagnostic agent composition may beadministered by injection, inhalation, ingestion, parenteral injection,or intravenous injection.

When used in diagnostic imaging, particularly of mammalian subjects andmore particularly of human subjects, the diagnostic agent compositionsprovided by the present invention, are typically administered as asuspension in a pharmaceutically acceptable carrier which may (but isnot required to) comprise one or more excipients. If the administrationis to be by injection, particularly parenteral injection, the carrier istypically an aqueous medium that has been rendered isotonic by theaddition of about 150 mM of NaCl, 5% dextrose or combinations thereof.It typically also has an appropriate (physiological) pH of between about7.3 and 7.4. The administration may be intravascular (IM), subcutaneous(SQ) or most commonly intravenous (IV). However, the administration mayalso be via implantation of a depot that then slowly releases thenanoparticles into the subject's blood or tissue. Alternatively, theadministration may be by ingestion for imaging of the GI tract or byinhalation for imaging of the lungs and airways.

The administration to human subjects, particularly intravenousadministration, requires that the diagnostic agent composition benon-toxic in the amounts used and free of any infective agents such asbacteria and viruses and also free of any pyrogens. Thus, thenanoparticle composition present in the diagnostic agent compositionshould be stable to the necessary purification procedures and not sufferdegradation in their hydrophilicity or change in the size of theconstituent nanoparticles.

In one embodiment, the present invention provides a diagnostic agentcomposition which may be delivered to the site of administration as astable aqueous colloidal suspension with the proper osmolality and pH,as a concentrated aqueous colloidal suspension suitable for dilutionprior to administration to a subject. In an alternate embodiment, thepresent invention provides a diagnostic agent composition as a powder,such as obtained by lyophilization, suitable for reconstitution.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal language of the claims.

EXPERIMENTAL SECTION Example 1 Synthesis of a Nanoparticulate MetalOxide Core (SPIO)

To a 20 mL solution of anhydrous benzyl alcohol, 0.706 g of iron (III)acetylacetonate (2 mmol) and 0.414 g of 1-phenyl-1,2-ethanediol (3 mmol)were added under stirring condition and the resulting mixture was heatedat 170° C. for 4 hrs. The reaction mixture was cooled to ambienttemperature to form a SPIO core solution containing 5.6 mg of Fe/mL.

Example 2 Synthesis of 1,2 Bis phosphate PEG 350 (1,2BPP350) (5)

A stirred solution of PEG350 monomethyl ether (35 g, 100 mmol) andtriethylamine (20.2 g, 200 mmol) in methylene chloride (200 mL) wascooled to 0° C., and methane sulfonyl chloride (17.1 g, 150 mmol) wasadded drop-wise. The reaction was then allowed to warm to roomtemperature and was stirred for an additional 3 h. A solution ofsaturated aqueous ammonium chloride (100 mL) was then added and thelayers were separated. The organic layer was washed with saturatedaqueous ammonium chloride (3×100 mL), saturated aqueous sodiumbicarbonate solution (1×100 mL), and finally with a saturated aqueoussodium chloride solution (1×100 mL). The organic solution was then driedover anhydrous sodium sulfate, filtered, and the solvent removed underreduced pressure to yield 48 g of compound 1 as an oil.

Freshly powdered potassium hydroxide (2.98 g, 53.1 mmol) was added toanhydrous DMSO (100 mL), and the mixture was stirred for 1 hour under aninert atmosphere. 1,2-isopropylideneglycerol (2.81 g, 21.3 mmol) wasthen added, followed by a drop-wise addition of PEG350 mesylate compound1 (9.1 g, 21.3 mmol) in 50 ml of anhydrous DMSO. The mixture was thenheated to 40° C. and stirred for 18 hours under inert atmosphere. Thereaction mixture was then cooled to ambient temperature, diluted withwater (200 mL), and extracted with methylene chloride (4×200 mL). Thecombined organic layers were then washed with water (2×200 mL) andconcentrated under reduced pressure yielding compound 2 as a yellow oil.¹H NMR (400 MHz, CDCl₃, δ): 4.3 (1H, m), 4.05-4.2 (2H, m), 3.5-3.75(32H, m), 3.4 (3H, s), 1.43 (3H, s), 1.37 (3H, s).

1N HCl in methanol (50 mL) was added to a stirred solution of 2 (8.8 g,21.4 mmol) in methanol (50 mL), and the reaction was stirred for 18 h atambient temperature. The mixture was then concentrated under reducedpressure and dried under high vacuum to yield 8 g of compound 3 as anoil. ¹H NMR (400 MHz, CDCl₃, δ): 3.95-4.0 (2H, bs), 3.9 (1H, m),3.55-3.8 (32H, s), 3.4 (3H, s).

Tetrazole (0.45M in acetonitrile, 32.4 mmol) was added to a solution ofdibenzyl N,N-diisopropylphosphoramidite (11.19 g, 32.4 mmol) inmethylene chloride (300 mL), and the mixture was stirred at ambienttemperature for 30 min. Diol compound 3 (3.0 g, 8.1 mmol) was then addedand the mixture was stirred for 18 h at ambient temperature. Thereaction was then cooled to −78° C. and m-chloroperoxybenzoic acid (77%)(59 g, 32.4 mmol) was added as a single portion. The reaction mixturewas then stirred at −78° C. for 10 minutes, allowed to warm to roomtemperature and then stirred for an additional 4 h. A 10% (w/v) aqueoussolution of sodium sulfite (100 mL) was then added and the layers wereseparated. The aqueous layer was back extracted with methylene chloride(100 mL) and the combined organic extracts were evaporated under reducedpressure. The resulting yellow oil was purified using columnchromatography (hexanes:ethyl acetate) followed by a solvent change(methylene chloride:methanol) yielding 4.58 g of compound 4. ¹H NMR (400MHz, CDCl₃, δ): 7.28-7.35 (20H, m), 5.0-5.1 (8H, m), 4.7 (1H, m),4.1-4.25 (2H, m), 3.55-3.8 (32H, m), 3.4 (3H, s).

Palladium on carbon (10%, 3 g) was added to a solution of compound 4(4.58 g, 5.14 mmol) in ethanol (100 mL) and the mixture was stirred atambient temperature under an H₂ atmosphere for 2 days. The reactionmixture was then filtered through celite and the filter cake was washedwith ethanol (2×50 mL). The filtrate was evaporated under reducedpressure yielding 6 g of compound 5 as a waxy solid. ¹H NMR (400 MHz,D₂0, δ): 4.38 (1H, bs), 3.9-4.0 (2H, m), 3.5-3.7 (32H, m), 3.27 (3H, s).

Example 3 Synthesis of Nanoparticle Composition (VII) (1,2BPP350 SPIO)

PEG350 Bisphosphate compound 5 (1.06 g, 2 mmol) was dissolved in 200 mMaqueous sodium hydroxide solution (20 mL). THF (20 mL) was then added,and the pH of the solution was adjusted to 8 by drop-wise addition of 3Msodium hydroxide. A solution of SPIO cores in benzyl alcohol (10 mL ofthe 5.6 mg Fe/mL solution) was then added, and the solution was stirredovernight at 50° C. The reaction was then cooled to ambient temperatureand diluted with hexanes (50 mL). The layers were separated and theaqueous layer was purified by tangential flow filtration (50K MWCOmembrane washed against 4 L of water) to provide a stable suspension ofthe nanoparticle composition VII. The final particles had a hydrodynamicdiameter of 9 nM as measured in a 150 mM sodium chloride solution bydynamic light scattering. The size of the particles did not change after2 days in the 150 mM sodium chloride solution incubated at 40° C.

Example 4 Synthesis of 1,2BPP350 Tantalum Oxide

Water (0.11 mL) was added to a stirred solution of compound 5 (3.92 g,7.4 mmol) dissolved in anhydrous methanol (75 mL), and the solution wasstirred for 20 minutes. Tantalum ethoxide (1.5 g, 3.69 mmol) was thenadded drop-wise, the mixture was stirred at ambient temperature for 1 h,and then heated at 50° C. for 18 h. The reaction was then cooled toambient temperature and diluted with water (250 mL). The pH was adjustedto ˜8 by the addition of ammonium hydroxide, the solution wasconcentrated until the methanol was fully evaporated, and the remainingaqueous solution was passed through a 100 nm filter. The particles werepurified using dialysis (3.5K MWCO PES membrane washed against 1 L ofwater with 4 exchanges). The retained solution was then passed through a100 nm filter yielding particles having a hydrodynamic size of 4.7 nM asmeasured in water by dynamic light scattering.

Example 5 Synthesis of 1,2BPP440 (10)

A solution of monodisperse decaethylene glycol monomethyl ether(Biomatrik; Zhejiang, China) (10 g, 21 mmol) and triethylamine (3.85 g,38 mmol) in methylene chloride (200 mL) was cooled to −30° C., andmethane sulfonyl chloride (3.64 g, 31.7 mmol) was added drop-wise. Thereaction was allowed to warm to 0° C. over 3 h. Saturated aqueousammonium chloride (100 mL) was then added and the layers were separated.The aqueous layer was back extracted with methylene chloride (50 mL),the combined organics washed with a saturated aqueous sodium bicarbonatesolution (1×100 mL), dried over magnesium sulfate, filtered, and thesolvent removed under reduced pressure to yield 12 g of compound 6 as anoil.

Freshly powdered potassium hydroxide (3.04 g, 54.3 mmol) was added toanhydrous DMSO (200 mL), and the mixture was stirred for 1.5 hours underan inert atmosphere. A solution of 1,2-isopropylideneglycerol (2.87 g,21.7 mmol) and PEG440 mesylate compound 6 (12.0 g, 21.7 mmol) in 20 mlof anhydrous DMSO was added, and the mixture was stirred for 18 hours at40° C. under inert atmosphere. The reaction mixture was then cooled toambient temperature, diluted with water (250 mL) and extracted withmethylene chloride (2×500 mL). The combined organic layers were thenwashed with water (1×500 mL) and concentrated under reduced pressureyielding compound 7 as a light yellow oil. ¹H NMR (400 MHz, CDCl₃, δ):4.3 (1H, m), 4.05-4.1 (1H, m), 3.7-3.8 (2H, m), 3.6-3.7 (39H, m),3.5-3.6 (4H, m), 3.4 (3H, s), 1.4 (6H, d).

1N HCl in methanol (50 mL) was added to a stirred solution of 7 (9.17 g,15.6 mmol) in methanol (50 mL). The reaction was stirred for 18 h atambient temperature, then concentrated under reduced pressure and driedunder high vacuum to yield 8.8 g of compound 8 as an oil. ¹H NMR (400MHz, CDCl₃, δ): 3.9 (1H, m), 3.65-3.8 (40H, s), 3.55-3.65 (4H, m), 3.4(3H, s).

Tetrazole (0.45M in acetonitrile, 22 mmol) was added to a solution ofdibenzyl N,N-diisopropylphosphoramidite (7.62 g, 22 mmol) in methylenechloride (300 mL), and the mixture was stirred at ambient temperaturefor 30 min. Diol compound 8 (3.0 g, 5.5 mmol) was then added, themixture was stirred for 18 h at ambient temperature. The reaction wasthen cooled to −78° C. and m-chloroperoxybenzoic acid (77%) (3.81 g, 22mmol) was added as a single portion. The reaction mixture was thenstirred at −78° C. for 10 minutes, allowed to warm to room temperatureand then stirred for an additional 4 h. A 10% (w/v) aqueous solution ofsodium sulfite (100 mL) was then added and the layers were separated.The aqueous layer was back extracted with methylene chloride (100 mL)and the combined organic extracts were evaporated under reducedpressure. The resulting oil was purified using column chromatography(hexanes:ethyl acetate) followed by a solvent change (methylenechloride:methanol) yielding 1.56 g of compound 9. ¹H NMR (400 MHz,CDCl₃, δ): 7.3-7.4 (20H, m), 5.0-5.1 (8H, m), 4.7 (1H, m), 4.1-4.25 (2H,m), 3.55-3.7 (42H, m), 3.4 (3H, s).

Palladium on carbon (10%) (0.25 g) was added to a stirred solution ofcompound 9 (1.56 g, 1.46 mmol) in ethanol (100 mL), and the mixture wasstirred at ambient temperature under an H₂ atmosphere for 2 days. Thereaction mixture was then filtered through celite and the filter cakewashed with ethanol (2×50 mL). The filtrate was evaporated under reducedpressure yielding 1.03 g of compound 10 as a clear oil. ¹H NMR (400 MHz,D₂O, δ): 4.395 (1H, m), 3.9-4.0 (2H, m), 3.5-3.65 (42H, m), 3.25 (3H,s).

Example 6 Synthesis of Nanoparticle Composition (VIII) (1,2BPP440 SPIO)

1M aqueous sodium hydroxide (3 mL) was added to a stirred solution ofcompound 10 (0.71 g, 2 mmol) dissolved in THF (20 mL) and water (15 mL).A solution of SPIO cores in benzyl alcohol (10 mL of the 5.6 mg Fe/mLsolution) was then added, and the mixture was stirred overnight at 50°C. The reaction was then cooled to ambient temperature and diluted withhexanes (2×50 mL). The layers were separated and the aqueous layer wasthen purified by tangential flow filtration (30K MWCO membrane washedagainst 4 L of water) to provide a stable suspension of the nanoparticlecomposition VIII. The final particles had a hydrodynamic diameter of10.3 nM as measured in water by dynamic light scattering. The size ofthe particles did not change after 2 days in 150 mM sodium chloridesolution incubated at 40° C.

Example 7 Synthesis of a 1,2BPP750 (15)

A solution of PEG750 monomethyl ether (75 g, 100 mmol) and triethylamine(30.3 g, 300 mmol) in methylene chloride (700 mL) was cooled to 0° C.,and methane sulfonyl chloride (22.8 g, 200 mmol) was added drop-wise.The resulting reaction was allowed to warm to room temperature and thenstirred for an additional 3 h. A solution of saturated aqueous ammoniumchloride (200 mL) was then added and the layers were separated. Theorganic layer was washed with saturated aqueous ammonium chloride (4×200mL), saturated aqueous sodium bicarbonate solution (1×200 mL), andfinally with a saturated aqueous sodium chloride solution (1×200 mL).The organic solution was then dried over anhydrous sodium sulfate,filtered, and the solvent removed under reduced pressure to yield 84 gof compound 11 as an oil. ¹H NMR (400 MHz, CDCl₃, δ): 4.36 (2H, m), 3.75(2H, m), 3.62 (64H, br. s), 3.55 (2H, m), 3.35 (3H, 3), 3.07 (3H, s).

Freshly powdered potassium hydroxide (12.75 g, 225 mmol) was added toanhydrous DMSO (150 mL), and the mixture was stirred for 30 minutesunder an inert atmosphere. 1,2-isopropylideneglycerol (26.4 g, 200 mmol)was then added, followed by a drop-wise addition of PEG mesylatecompound 11 (84 g, 100 mmol) in 500 ml of anhydrous DMSO. The mixturewas stirred for three days under inert atmosphere. A mixture of 80%aqueous sodium chloride (700 mL) and methylene chloride (500 mL) wasthen added, the layers were separated, and the aqueous layer wasback-extracted with methylene chloride (4×300 mL). The combined organiclayers were then washed with saturated sodium chloride (1×500 mL), driedover anhydrous sodium sulfate, and filtered. The solvent was removedunder reduced pressure, and the remaining DMSO was distilled off underhigh vacuum. The material was then dissolved in warm THF (200 mL) andheptane (75 mL), a small amount of solid was filtered off, and thefiltrate was allowed to crystallize overnight at 5° C. At this time,cold heptane (200 mL) was added, the solid was collected via coldfiltration. Residual 1,2-isopropylideneglycerol was removed bydissolving the material in water (700 mL) and washing with heptane(5×150 mL), yielding product compound 12 in aqueous solution. Thesolvent was removed from a small aliquot of the aqueous solution,yielding solid compound 12. ¹H NMR (400 MHz, CDCl₃, δ): 4.15 (1H, m),3.92 (1H, m), 3.3-3.7 (68H, m), 3.25 (3H, s), 1.25 (6H, d).

The resulting aqueous solution of compound 12 (700 mL) was mixed with 3NHCl (100 mL), and stirred overnight. The majority of the water was thenstripped off via rotary evaporation, and the remaining material wassuspended in methylene chloride (600 mL). Solid anhydrous sodiumcarbonate (50 g) was then added cautiously, and the mixture stirred for1 hour. The solid was filtered off, and the solvent removed via rotaryevaporation. Toluene (300 mL) was then added and the solution wasrefluxed for 2 hours with a Dean Stark trap to remove any remainingwater. The solution was then cooled to room temperature, the toluene wasstripped off by rotary evaporation, and the remaining material was driedunder hi vacuum to yield 72 g of compound 13 as an oily solid. ¹H NMR(400 MHz, CDCl₃, δ): 3.78 (2H, m), 3.45-3.7 (68H, m), 3.35 (3H, s).

Tetrazole (0.45M in acetonitrile, 72.8 mmol) was added to a solution ofdibenzyl N,N-diisopropylphosphoramidite (25.1 g, 72.8 mmol) in methylenechloride (200 mL), and the mixture was stirred at ambient temperaturefor 30 min. Diol compound 13 was then added (15 g, 18.2 mmol) and theresulting mixture was stirred for 18 h at 40° C. The reaction was thencooled to −35° C., and m-chloroperoxybenzoic acid (77%) (12.6 g, 72.8mmol) was added as a single portion. The reaction was then stirred at−35° C. for 5 min, allowed to warm to room temperature, and then stirredfor an additional 4 h. A 10% (w/v) aqueous solution of sodium sulfite(100 mL) was then added, the reaction was stirred for 30 min, the layerswere separated, and the organic layer evaporated under reduced pressure.The resulting yellow oil was purified using column chromatography(hexanes:ethyl acetate) followed by a solvent change (methylenechloride:methanol) yielding 8 g of compound 14 as a clear oil. ¹H NMR(400 MHz, CDCl₃, δ): 7.3-7.4 (20H, m), 5.0-5.1 (8H, m), 4.65 (1H, m),4.1-4.25 (2H, m), 3.55-3.8 (70H, m), 3.4 (3H, s).

Palladium on carbon (10%) (0.5 g) was added to a stirred solution ofcompound 14 (8 g, 5.8 mmol) in ethanol (100 mL), and the mixture wasstirred at ambient temperature under an H₂ atmosphere for 2 days. Thereaction mixture was then filtered through celite and the filter cakewas washed with ethanol (2×50 mL). The filtrate was evaporated underreduced pressure yielding 6 g of compound 15 as a waxy solid. ¹H NMR(400 MHz, CDCl₃, δ): 4.75 (1H, bs), 4.1-4.3 (2H, m), 3.55-3.8 (70H, m),3.4 (3H, s).

Example 8 Synthesis of Nanoparticle Composition (IX) (1,2BPP750 SPIO)

1M aqueous sodium hydroxide solution (0.6 mL) was added to a stirredsolution of PEG750 bisphosphate compound 15 (0.203 g, 0.2 mmol)dissolved in THF (4 mL) and water (2.5 mL). A solution of SPIO cores inbenzyl alcohol (4 mL of a 2.8 mg Fe/mL solution) was then added, and thesolution was stirred overnight at 50° C. The reaction was then cooled toambient temperature and diluted with hexanes (10 mL). The layers wereseparated and the aqueous layer was then purified using centrifugefilters (30K MWCO washed against water) to provide a stable suspensionof the nanoparticle composition IX. The final particles had ahydrodynamic diameter of 13 nM as measured in a 150 mM sodium chloridesolution by dynamic light scattering. The size of the particles did notchange after 2 days in 150 mM sodium chloride solution incubated at 40°C. The material could be sterilized by autoclave (121° C., 15 minutes,5% mannitol formulation) with no sign of aggregation or change inparticle size.

Example 9 Synthesis of a 1,2BPP2000 (20)

A solution of PEG1900 monomethyl ether (95 g, 50 mmol) and triethylamine(20.2 g, 200 mmol) in methylene chloride (700 mL) was cooled to 0° C.,and methane sulfonyl chloride (17.1 g, 150 mmol) was added drop-wise.The resulting reaction was allowed to warm to room temperature and thenstirred for an additional 18 h. A solution of saturated aqueous ammoniumchloride (200 mL) was then added and the layers were separated. Theorganic layer was washed with saturated aqueous ammonium chloride (4×200mL), saturated aqueous sodium bicarbonate solution (1×200 mL), andfinally with a saturated aqueous sodium chloride solution (1×200 mL).The organic solution was then dried over anhydrous sodium sulfate,filtered, and the solvent removed under reduced pressure, yielding 100 gof compound 16 as a white solid. ¹H NMR (400 MHz, CDCl₃, δ): 4.38 (2H,m), 3.75 (2H, m), 3.62 (176H, br. s), 3.55 (2H, m), 3.38 (3H, 3), 3.10(3H, s).

Freshly powdered potassium hydroxide (11.2 g, 200 mmol) was added toanhydrous DMSO (150 mL), and the mixture was stirred for 30 minutesunder an inert atmosphere. 1,2-isopropylideneglycerol (26.4 g, 200 mmol)was then added, followed by a drop-wise addition of PEG2000 mesylatecompound 16 (100 g, 50 mmol) in 500 ml of anhydrous DMSO. The mixturewas then stirred for three days under inert atmosphere. 80% aqueoussodium chloride (700 mL) and methylene chloride (500 mL) were thenadded, the layers were separated, and the aqueous layer wasback-extracted with methylene chloride (4×300 mL). The combined organicsolution was then washed with saturated sodium chloride (1×500 mL),dried over anhydrous sodium sulfate, and filtered. The solvent wasremoved under reduced pressure, and the remaining DMSO was distilled offunder high vacuum. The material was then dissolved in hot THF (300 mL)and heptane (100 mL), a small amount of solid was filtered off, and thefiltrate was allowed to crystallize overnight at 5° C. Cold heptane (200mL) was then added, and the solid was collected via cold filtration. Thesolid was recrystallized a second time from comparable amounts ofsolvent, and the product was dried yielding 86 g of compound 17 as asolid. ¹H NMR (400 MHz, CDCl₃, δ): 4.25 (1H, m), 4.00 (1H, m), 3.4-3.8(172H, m), 3.33 (3H, s), 1.35 (6H, d)

3N HCl (100 mL) was added to a stirred solution of compound 17 (86 gm)in water (600 mL), and the mixture was stirred overnight. The majorityof the water was then stripped off via rotary evaporation, and theremaining material was suspended in methylene chloride (600 mL). Solidanhydrous sodium carbonate (50 g) was then cautiously added, and themixture stirred for 1 hour. The solid was then filtered off, and thesolvent was removed from the filtrate via rotary evaporation. Toluene(300 mL) was then added and the mixture was refluxed for 2 hours with aDean Stark trap to collect any remaining water. The mixture was thencooled to room temperature, the toluene was removed under reducedpressure, and the remaining material was dried under hi vacuum, yielding75 g of compound 18 as a solid. ¹H NMR (400 MHz, CDCl₃, δ): 3.78 (2H,m), 3.45-3.7 (185H, m), 3.30 (3H, s).

Tetrazole (0.45M in acetonitrile, 40.5 mmol) was added to a solution ofdibenzyl N,N-diisopropylphosphoramidite (14 g, 40.5 mmol) in methylenechloride (200 mL), and the mixture was stirred at ambient temperaturefor 30 min. Diol compound 18 was added (20 g, 10.1 mmol) and theresulting mixture was stirred for 2d at 40° C. The reaction was thencooled to −35° C., and m-chloroperoxybenzoic acid (77%) (6.98 g, 40.5mmol) was added as a single portion. The reaction was stirred at −35° C.for 5 min, then allowed to warm to room temperature and stir for anadditional 4 h. A 10% (w/v) aqueous solution of sodium sulfite (100 mL)was then added, the reaction was stirred for 30 min, the layersseparated, and the organic layer was evaporated under reduced pressure.The resulting yellow oil was purified using column chromatography(hexanes:ethyl acetate) followed by a solvent change (methylenechloride:methanol) yielding 15 g of compound 19 as a solid. ¹H NMR (400MHz, CDCl₃, δ): 7.29-7.35 (20H, m), 5.0-5.1 (8H, m), 4.65 (1H, m),4.1-4.25 (2H, m), 3.5-3.75 (184H, m), 3.4 (3H, s).

Palladium on carbon (10%) (0.5 g) was added to a stirred solution ofcompound 19 (15 g, 5.9 mmol) in ethanol (100 mL), and the mixture wasstirred at ambient temperature under an H₂ atmosphere for 2d. Thereaction mixture was then filtered through celite and the filter cakewashed with ethanol (2×50 mL). The filtrate was evaporated under reducedpressure yielding 11.8 g of compound 20 as a waxy solid. ¹H NMR (400MHz, CDCl₃, δ): 4.75 (1H, bs), 4.2-4.3 (2H, m), 3.55-3.85 (184H, m), 3.4(3H, s).

Example 10 Synthesis of Nanoparticle Composition (X) (1,2BPP2000 SPIO)

A 1M aqueous sodium hydroxide solution (0.6 mL) was added to a stirredsolution of PEG2000 bisphosphate compound 20 (0.440 g, 0.2 mmol) in THF(4 mL) and water (2.5 mL). A solution of SPIO cores in benzyl alcohol (4mL of a 2.8 mg Fe/mL solution) was then added, and the mixture wasstirred overnight at 50° C. The reaction was then cooled to ambienttemperature and diluted with hexanes (10 mL). The layers were separatedand the aqueous layer was then purified via centrifuge filtration (30KMWCO washed against water) to provide a stable suspension of thenanoparticle composition X. The final particles had a hydrodynamicdiameter of 16 nM as measured in a 150 mM sodium chloride solution bydynamic light scattering. The size of the particles did not change after2 days in 150 mM sodium chloride solution incubated at 40° C. Thematerial could be sterilized by autoclave (121° C., 15 minutes) with nosign of aggregation or change in particle size

Example 11 Synthesis of a Mannitol-Based Phosphorylated polyol “P2P4Man”(23)

Freshly powdered potassium hydroxide (0.47 g, 8.4 mmol) in anhydrousDMSO (30 mL) was stirred for 30 minutes under an inert atmosphere.Mannitol (0.182 g, 1 mmol) was then added, followed by PEG440 mesylatecompound 6 (2.2 g, 4 mmol). The mixture was stirred for three days underinert atmosphere. 80% saturated aqueous sodium chloride (100 mL) andmethylene chloride (100 mL) were then added, the layers were separated,and the aqueous layer was back-extracted with methylene chloride (4×75mL). The combined organic solution was then washed with saturated sodiumchloride (1×100 mL), dried over anhydrous sodium sulfate, and filtered.The filtrate was removed under reduced pressure, and the remaining DMSOwas distilled off under high vacuum yielding 2.3 g of compound 21 as athick oil. ¹H NMR (400 MHz, CDCl₃, δ): 3.5-3.9 (44H, m), 3.39 (3H, s)indicated structure 21 wherein the groups O—R² are principally hydroxygroups and PEG groups O(CH₂CH₂O)₁₀CH₃ and wherein the ratio of hydroxygroups to PEG groups is approximately 2.2 to 3.8.

Tetrazole (0.45M in acetonitrile, 4 mmol) was added to a solution ofdibenzyl N,N-diisopropylphosphoramidite (1.38 g, 4 mmol) in methylenechloride (15 mL), and the mixture was stirred at ambient temperature for30 min. Diol compound 21 (2.3 g, 1 mmol) in 25 mL of methylene chloridewas then added, and the resulting mixture was stirred for 3d at ambienttemperature under an inert atmosphere. The solution was then cooled to−78° C. and m-chloroperoxybenzoic acid (77%) (0.9 g, 4 mmol) in 10 mL ofmethylene chloride was added. The reaction was then allowed to warm toroom temperature over 2 h with stirring. A 10% (w/v) aqueous solution ofsodium sulfite (20 mL) was then added, the reaction was stirred for 30min, the layers were separated and the aqueous layer was back extractedwith methylene chloride (2×20 mL). The combined organic layers werewashed with saturated sodium chloride (50 mL), dried over sodiumsulfate, filtered and the filtrate evaporated under reduced pressure.The resulting product was purified using column chromatography(hexanes:ethyl acetate) followed by a solvent change (methylenechloride:methanol) yielding 0.7 g of compound 22 the structure of whichwas confirmed by ¹H NMR (400 MHz, CDCl₃, δ): 7.25 (5.85H, m), 5.0(2.34H, m), 3.9-3.5 (43H, m), 3.39 (3H, 3). NMR integration indicatedthat the groups O—R² were principally dibenzyl phosphate groups(PhCH₂O)₂PO₂ groups and PEG groups O(CH₂CH₂O)₁₀CH₃, and that the ratioof phosphorus to PEG was 0.58, with approximately 3.8 PEG groups andapproximately 2.2 dibenzyl phosphate groups per molecule.

A solution of compound 22 (0.7 g) in methanol (20 mL) was sparged withnitrogen for 2 minutes, then palladium on carbon (10%) (0.07 g) wasadded. The reaction was stirred at ambient temperature under an H₂atmosphere for 18 h, after which time TLC analysis indicated that thereaction was complete. The reaction mixture was filtered through celiteand the filtrate was evaporated under reduced pressure yielding 0.59 gof compound 23. ¹H NMR (400 MHz, CDCl₃, δ): 4.2-3.5 (44H, m), 3.40 (3H,3) indicated that the groups O—R² were principally phosphate groups(HO)₂PO₂ groups and PEG groups O(CH₂CH₂O)₁₀CH₃, with approximately 3.8PEG groups and approximately 2.2 phosphate groups per molecule.

Example 12 Synthesis of Nanoparticle composition “P2P4Man” SPIO

A reaction vial was charged with water (2 mL), compound 23 (0.214 g) and5N NaOH (50 uL). The contents were shaken until fully dissolved,yielding a solution with pH=8.0. The mixture was then lyophilized, andthe residue was dissolved in THF (10 mL). A solution of SPIO core inbenzyl alcohol (2.3 mL, 5.5 mg Fe/mL) was then added, and the solutionwas capped and stirred overnight at 50° C. Water (6 mL) was then added,the mixture was shaken, and the dark color transferred completely intothe aqueous layer. The layers were separated, and the aqueous layersolution was washed with hexane (2 mL) and filtered through a 20 nmfilter. The solution was then syringed into a 3500 MW dialysis cassette,and the dialyzed against water (1 L) for 24 hours, changing the dialysisbath water 4 times over the course of the dialysis to provide a stablesuspension of nanoparticle composition wherein R² is. The finalparticles had a hydrodynamic diameter of 11 nM as measured in a 150 mMsodium chloride solution by dynamic light scattering. The size of theparticles did not change after 3 days in the 150 mM sodium chloridesolution incubated at 40° C.

Example 13 Synthesis of a 1,3BPP350 (27)

Freshly powdered potassium hydroxide (1.03 g, 18.4 mmol) in anhydrousDMSO was stirred for 1 hour under an inert atmosphere.1,3-dibenzyloxy-2-propanol (2.0 g, 7.34 mmol) and PEG350 mesylatecompound 1 (3.14 g, 7.34 mmol) in 15 ml of anhydrous DMSO were thenadded, and the mixture was stirred at 40° C. for 18 hours under an inertatmosphere. The reaction mixture was then cooled to ambient temperature,diluted with water (100 mL) and extracted with methylene chloride (2×150mL). The combined organic layers were then washed with water (2×50 mL)and concentrated under reduced pressure yielding compound 24 as a yellowoil.

Palladium on carbon (10%) (0.41 g) was added to a stirred solution ofcompound 24 (4.5 g, 7.34 mmol) in dry methanol (150 mL), followed by an88% formic acid solution (5 mL). The mixture was then stirred for 18 hat ambient temperature. The reaction mixture was then filtered throughcelite and the filter cake washed with methanol (2×50 mL). The filtratewas evaporated under reduced pressure yielding 2.7 g of compound 25 as aclear oil. ¹H NMR (400 MHz, CDCl₃, δ): 3.8-3.9 (2H, m), 3.5-3.8 (32H,m), 3.4 (3H, s).

Tetrazole (0.45M in acetonitrile, 29.4 mmol) was added to a solution ofdibenzyl N,N-diisopropylphosphoramidite (10.14 g, 29.4 mmol) inmethylene chloride (200 mL), and the mixture was stirred at ambienttemperature for 30 min Diol compound 25 (2.7 g, 7.34 mmol) was thenadded, and the resulting mixture was stirred for 18 h at ambienttemperature. The reaction mixture was then cooled to −78° C., andm-chloroperoxybenzoic acid (77%) (5.07 g, 29.4 mmol) was then added as asingle portion. The mixture was stirred at −78° C. for 10 minutes,allowed to warm to room temperature and stirred for an additional 4 h. A10% (w/v) aqueous solution of sodium sulfite (100 mL) was then added andthe layers were separated. The aqueous layer was back extracted withmethylene chloride (100 mL) and the combined organic extracts wereevaporated under reduced pressure. The resulting product was utilizedwithout further purification as yellow oil compound 26. ¹H NMR (400 MHz,CDCl₃, δ): 7.3-7.45 (20H, m), 4.98-5.1 (8H, m), 3.95-4.2 (4H, m),3.5-3.7 (28H, m), 3.4 (3H, s).

Palladium hydroxide (0.2 g) was added to a stirred solution of compound26 (4.18 g, 4.69 mmol) in ethanol (100 mL), and the mixture was stirredat ambient temperature under an H₂ atmosphere for 2 days. The reactionmixture was then filtered through celite and the filter cake was washedwith ethanol (2×50 mL). The filtrate was then evaporated under reducedpressure yielding 2.5 g of compound 27 as a clear oil. ¹H NMR (400 MHz,CDCl₃, δ): 3.85-4.0 (3H, m), 3.7-3.8 (2H, m), 3.5-3.65 (28H, m), 3.27(3H, s).

Example 14 Synthesis of Nanoparticle Composition (XVI) (1,3BPP350 SPIO)

THF (1 mL) was added to a stirred solution of compound 27 (0.106 g, 0.2mmol) in 200 mM aqueous sodium hydroxide solution (1 mL). The pH wasthen adjusted to 8 by drop-wise addition of a 3M sodium hydroxidesolution. A solution of SPIO cores in benzyl alcohol (1 mL of a 5.6 mgFe/mL solution) was then added, and the mixture was stirred overnight at50° C. The reaction was then cooled to ambient temperature, the layersseparated and the aqueous layer was then purified using dialysis (10KMWCO PES membrane washed against 1 L of water with 4 exchanges). Theretained solution was then passed through a 100K MWCO centrifugemembrane to remove any remaining aggregates to provide a stablesuspension of nanoparticle composition XVI. The final particles had ahydrodynamic diameter of 9.5 nM as measured in a 150 mM sodium chloridesolution by dynamic light scattering.

Example 15 Synthesis of a 1,3BPP2000 (31)

Freshly powdered potassium hydroxide (960 mg, 17.1 mmol) in anhydrousDMSO (10 mL) was stirred for 20 min under an inert atmosphere.2-Phenyl-1,3-dioxan-5-ol (3.08 gm g, 17.1 mmol) and PEG2000 mesylatecompound 16 (8.55 g, 4.27 mmol) in DMSO (80 mL) were then added, and themixture was stirred for 18 hours at room temperature under an inertatmosphere. A 90% saturated sodium chloride solution (150 mL) andmethylene chloride (100 mL) were then added, and the layers wereseparated. The aqueous layer was extracted with methylene chloride (2×75mL). The combined organic layers were then washed with saturated sodiumchloride (75 mL), dried over anhydrous sodium sulfate, filtered, andthen concentrated under reduced pressure yielding compound 28 as ayellow oily solid. Excess DMSO was distilled off under hi vacuum, andthe remaining solid was recrystallized from a mixture of hot THF (100mL) and hot hexane (40 mL). ¹H NMR (400 MHz, CDCl₃, δ): 7.50 (2H, m),7.38 (3H, m) 5.58 (1H, s), 4.38 (2H, m), 4.05 (2H, m), 3.9-3.5 (176H,m), 3.39 (3H, s).

Palladium hydroxide (0.5 g) was added to a stirred solution of compound28 (4.18 g, 4.69 mmol) in ethanol (100 mL), and the mixture was stirredat ambient temperature under an H₂ atmosphere for 18 hours. The mixturewas then filtered through celite and the filter cake was washed withethanol (2×50 mL). The filtrate was evaporated under reduced pressureyielding 5.0 g of compound 29 as a white sticky solid. ¹H NMR (400 MHz,CDCl₃, δ): 3.85 (3H, m), 3.5-3.75 (178H, m), 3.38 (3H, s).

Tetrazole (0.45M in acetonitrile, 10.1 mmol) was added to a solution ofdibenzyl N,N-diisopropylphosphoramidite (3.5 g, 10.1 mmol) in methylenechloride (100 mL), and the mixture was stirred at ambient temperaturefor 30 min. Diol compound 29 was then added (5.0 g, 2.53 mmol) and theresulting mixture was stirred for 48 h at 40° C. The reaction was thencooled to −35° C. and tert-butylhydroperoxide (90%) (0.91 g, 10.1 mmol)was added as a single portion. The reaction mixture was then stirred at−35° C. for 10 minutes, allowed to warm to room temperature, and thenstirred for an additional 4 h. A 10% (w/v) aqueous solution of sodiumsulfite (100 mL) was then added and the layers were separated. Theaqueous layer was back extracted with methylene chloride (100 mL) andthe combined organic extracts were evaporated under reduced pressure.The resulting product was utilized without further purification asyellow oil compound 30.

bisdibenzyl phosphate 30 was converted to bisphosphate 31 as taught inExample 13 herein.

Comparative Example 1 Synthesis of a PEG2000 monophosphate (33)

A solution of PEG1900 monomethyl ether in methylene chloride containingan excess of triethylamine and catalytic 4-dimethylaminopyridine (DMAP)was treated with an excess of diphenyl chlorophosphate. The mixture wasstirred for 24 hours under nitrogen, quenched by the addition of anexcess of 1N hydrochloric acid, and the layers were separated. Theorganic layer was washed once with water, the solvent was distilled offfirst at atmospheric pressure, then at reduced pressure, toazeoptropically remove any remaining water. The residue was crystallizedfrom a mixture of hot THF and hexanes, then was washed with methyltert-butyl ether. After drying under vacuum, the product was redissolvedin tetrahydrofuran and treated with activated charcoal. The charcoal wasfiltered off, and the solution was diluted with hexanes, cooled, and theprecipitated product collected by filtration. The solids were washedwith methyl tert-butyl ether and hexanes, then dried under vacuum for a70-90% yield of product PEG2000 monophosphate diphenyl ester 32.

A solution of the PEG2000 monophosphate diphenyl ester 32 in acetic acidwas hydrogenated at 45° C. and 2-4 bar pressure in the presence of 5mole % platinum oxide until the hydrogen uptake ceased. After cooling,the catalyst was removed by filtration, the filtrate was concentratedunder reduced pressure and the residue was dissolved in tetrahydrofuran.Hexanes were added, the mixture was cooled, the precipitated product wascollected by filtration, and the solid was washed with methyl tert-butylether and hexanes. The product monophosphate 33 was then dried undervacuum at ambient temperatures for a 70-90% yield of product. Thismaterial was not stable to autoclave sterilization, whereas the 1,2 and1,3-BPP2000 materials were shown to be stable under comparable autoclaveconditions.

Comparative Example-2 Synthesis of a PEG2000 Monophosphate Coated SPIO

PEG2000 monophosphate (14.57 g, 7.0 mmol) prepared in ComparativeExample 1 was suspended in THF (161 mL) and a solution of SPIOnanoparticles (35 mL at 5.6 mg Fe/mL in benzyl alcohol) was added. Theresulting suspension was stirred at 50° C. for 16 h during which thereaction became homogeneous. The reaction was then cooled to roomtemperature and diluted with water (200 mL). The resulting layers wereseparated and the aqueous layer was washed with hexanes (2×200 mL). Theremaining volatiles were removed from the aqueous layer in vacuo and theresulting aqueous nanoparticle suspension was washed against a 100 kDaMWCO tangential flow filtration membrane with water (3.75 L) to providea suspension of The resulting nanoparticles had a hydrodynamic diameterof 18.7 nm in 150 mM NaCl at 25° C. as measured by dynamic lightscattering.

Comparative Example 3 Autoclave stability of PEG2000 MonophosphateCoated SPIO

A suspension of PEG2000 monophosphate coated SPIO nanoparticles preparedin Comparative Example 2 (1 mL at 10 mg Fe/mL) in water were autoclavedin a closed, 2 dram glass vial at 121° C. and 20 atm for 15 min. Afterthe autoclave cycle was complete, all color had precipitated from thesolution, indicating complete aggregation of the nanoparticles.

Comparative Example 4 Synthesis of a PEG350 monophosphate Coated SPIO(XVII)

A solution of PEG-350 mono(methyl ether) (8.54 g, 24.4 mmol) dissolvedin CH₂Cl₂ (80 mL) was charged with triethyl amine (3.68 g, 36.6 mmol)followed by 4-N,N-dimethylaminopyridine (0.298 g, 2.44 mmol). Theresulting solution was cooled to 0° C., diphenyl chlorophosphate (7.87g, 29.3 mmol) was added dropwise, and the reaction was stirred at 0° C.for 10 min. The reaction was then warmed to room temperature and stirredfor an additional 16 h. The reaction was quenched by the addition of 10%HCl (80 mL) and the resulting layers were separated. The organic layerwas washed with water (80 mL) and brine (80 mL) and dried over anhydrousMgSO₄. Filtration and removal of the solvent in vacuo afforded the monophosphate diphenyl ester of PEG-350 mono(methyl ether) (14.2 g, 100%) asa golden oil. ¹H NMR (400 MHz, CDCl₃, δ): 7.34 (m, 4H), 7.22 (m, 6H),4.38 (m, 2H), 3.73 (m, 2H), 3.64 (m, 24H), 3.54 (m, 2H), 3.38 (s, 3H).

Platinium^(IV) oxide hydrate (200 mg) was added to a solution of themono phosphate diphenyl ester of PEG-350 mono(methyl ether) preparedabove (14.2 g, 24.4 mmol) dissolved in acetic acid, and the resultingsuspension was heated to 50° C. and placed under an atmosphere of H₂until hydrogen uptake ceased. The reaction was filtered through a celitepad to remove catalyst and the solvent was removed in vacuo to leave thedesired product mono phosphate of PEG-350 mono(methyl ether) (10.49 g,100%) as a clear, yellow oil. ¹H NMR (400 MHz, CDCl₃, δ): 4.20 (m, 2H),3.67 (m, 24H), 3.56 (m, 2H), 3.39 (s, 3H).

To a colloidal suspension of superparamagnetic iron oxide nanoparticles(SPIO cores solution in benzyl alcohol) diluted to 1 mg Fe/mL with THFwas added the mono phosphate of PEG-350 mono(methyl ether) (2 mol ofphosphate groups per mol of Fe) and the resulting suspension was heatedat 50° C. for 16 h. The reaction was then cooled to room temperature,diluted with water, and the brown aqueous solution was washed threetimes with hexanes. Any remaining volatiles in the aqueous layer wereremoved in vacuo and the resulting nanoparticles were purified bywashing with H₂O against a 30 kDa molecular cutoff filter usingtangential flow filtration to provide a suspension of nanoparticlecomposition XVII. The particles had a hydrodynamic diameter of 50 nm, asmeasured by dynamic light scattering. After 1 week of storage in waterthe particles had a hydrodynamic diameter greater than 100 nm.

Comparative Example 5 Comparison of Stability of 1,2-bisphosphate,1,3-bisphosphate, and monophosphate Coated SPIOs

Data are gathered in the Table below which compare the properties ofnanoparticle compositions provided by the present invention with ananoparticle composition not comprising a phosphorylated polyolcomprising at least two phosphate groups, the PEG-350 phosphate. Theeffect of a “second” phosphate group is striking in that it renders thenanoparticle composition both more stable in terms if change inhydrodynamic diameter (D_(H)) as determined by dynamic light scattering.

TABLE Stability and Zeta Potential of Coated SPIOs D_(H) post D_(H) 2weeks post Zeta Nanoparticle Coating synthesis synthesis PotentialPEG-350 Phosphate*  50 ± 1 nm  >100 nm   7.3 mV 1,2-BPP350 SPIO†   9 ± 1nm   9 ± 1 nm −5.0 mV 1,3-BPP350 SPIO† 9.5 ± 1 nm 8.4 ± 1 nm −1.7 mV*mono phosphate (also referred to herein as the mono phosphate ofPEG-350 mono(methyl ether), †bisphosphate

Additional data are gathered in the following Table which furtherillustrate the advantages of the nanoparticle compositions provided bythe present invention. The data highlight the importance of having atleast two phosphate groups present in the phosphorylated polyol used tostabilize the nanoparticulate metal oxide (here nanoparticulatesuperparamagnetic iron oxide, referred to simply as SPIO or SPIOs) andthe advantages provided by stabilizers comprising two phosphate groupsand one or more hydrophilic groups of the polyalkylene ether type, forexample polyethylene ether groups derived from the mono methyl ether ofPEG350 or the mono methyl ether of PEG2000. Significantly, at least someof the nanoparticle compositions provided by the present invention arestable under autoclaving conditions, which characteristic may serve as athreshold indicator of suitability for a material's use in human medicalimaging techniques. It is emphasized that the data presented are fornanoparticle compositions comprising the indicated stabilizer compoundsas opposed to the stabilizer compounds themselves in the absence of thenanoparticulate metal oxide.

TABLE Stability of Coated SPIOs As A Function Of Stabilizer Structure1,2-Bisphosphate Stabilizer Monophosphate Stabilizer 1,2-BPP350PEG350-monophosphate D_(H) = 9 nm D_(H) = >50 nm Stable in 150 mM salineUnstable in 150 mM saline solution, 2 days at 40° C. solution, 2 days at40° C. TFF stable Unstable to TFF 1,2-BPP2000 PEG2000-monophosphateD_(H) = 16 nm D_(H) = 22 nm Stable in 150 mM saline Stable in 150 mMsaline solution, 2 solution, 2 days at 40° C. days at 40° C. TFF stableTFF stable Autoclave stable, 121° C. 15 min Unstable to autoclave, 121°C. 15 min ‡Tangential Flow Filtration (purification)

Example 16 In Vivo Imaging of Tumors by MRI

All procedures involving animals were completed under protocols approvedby the GE Global Research Institutional Animal Care and Use Committee.Tumors were induced in female Fischer 344 rats (˜150 g) by subcutaneousinjection of 2×10⁶ Mat B III cells (ATCC#CRL1666, ATCC, Manassas, Va.)in 0.1 mL Hank's balanced saline solution. The injection site waslocated dorsally between the shoulder blades. The tumors were imaged 12days after implantation, when the tumors were ˜1 cm in diameter.

Imaging was conducted on a clinical 3 Tesla GE MR750 scanner using acustom-built, ˜6 cm solenoid receiver RF coil. To prepare for imaging,the rats were anesthetized by IP injection of ketamine and diazepamusing 55 and 3.8 mg/kg doses, respectively. Once immobile, a salineprimed 1 F tail vein catheter (MTV-02, Strategic Applications Inc.,Libertyville, Ill.) was placed in a lateral tail vein and secured withtape. The prepared animal was then placed within the RF coil andpositioned within the bore of the scanner. A pre-injection image set wasacquired, and then, without moving the table or the animal, the 1-2bisphosphate-PEG (Mw=2 kDa) coated superparamagnetic iron oxidenanoparticles were injected via the catheter by a saline flush (˜0.4mL). Following injection, image sets were collected throughout a dynamicacquisition period of ˜30 minutes. For the injection, the nanoparticlecomposition (SPIO agent) was formulated in 5% aqueous mannitol at aconcentration of 2 mg Fe/mL and was dosed at 2 mg Fe/kg body weight.

A 3D fast gradient echo pulse sequence was employed that allowedsimultaneous collection of images at 10 echo times. The imaging slab waspositioned via the graphical prescription interface such that the tumorwas centered within the transaxial slices and the coverage included themajority of the tumor in depth. The pulse sequence parameters were asfollows: pulse sequence: 3D ME fGRE; TE: ranged from 4.0 to 65.4 ms,with 6.8 ms spacing; TR: 70.4 ms; flip angle: 25 degrees; bandwidth:62.5 MHz; matrix: 256×192; slice thickness: 0.6 mm; field of view: 9 cm,yielding a voxel size of 0.35×0.35×0.6 mm. The sequence acquisition timewas ˜2 min.

The imaging data sets were analyzed using a custom software tool(CineTool v8.0.2, GE Healthcare) built upon the IDL platform (IDL v.6.3, ITT Corp., Boulder, Colo.). In brief, the image analysis toolallowed manual drawing of 3D regions of in interest (ROIs) on thepre-injection series with subsequent calculation of the T₂* timeconstant and extrapolated intensity at TE=0 by exponential regressionfor every voxel within the drawn ROIs at all time points. These datawere used for estimation of physiologic parameters including tumor bloodvolume and vascular permeability. Representative images and differencemaps are given in FIG. 2. The FIG. 2 illustrates the representativeT1-weighted images (TE=4.0 ms) before injection of the iron oxidenanoparticle composition (A) and 30 min following injection of the ironoxide nanoparticle composition (B). The tumor region (arrow) shows moreenhancement than muscle (arrow head), as demonstrated by signalintensity difference map (C). T2*-weighted images (TE=24.5 ms) for thesame slice before administration of iron oxide nanoparticle composition(D) and 15 m following the administration of iron oxide nanoparticlecomposition (E). Difference map of the R²* relaxation rate (F) exhibitsdifferentiation of tumor from muscle tissue.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

What is claimed is:
 1. A nanoparticle composition comprising: ananoparticulate iron oxide core; and a shell comprising a phosphorylatedpolyol comprising at least two phosphate groups, wherein at least two ofthe phosphate groups occupy positions in the phosphorylated polyol whichconstitute a 1,2 or 1,3 spatial relationship to one another and thepolyol comprises a hydrophilic group selected from the group consistingof polyethylene ether moieties, polypropylene ether moieties,polybutylene ether moieties, and combinations of two or more of theforegoing hydrophilic moieties.
 2. The composition of claim 1, whereinthe nanoparticulate iron oxide core comprises superparamagnetic ironoxide.
 3. The composition of claim 1, wherein the phosphorylated polyolcomprises at least one of an ester group, amide group, a carbamategroup, a urea group, or a carbonate group.
 4. The composition of claim1, characterized by an average hydrodynamic diameter (D_(H)) asdetermined by dynamic light scattering in 150 mM NaCl water in a rangefrom about 2 nm to about 500 nm.
 5. The nanoparticle composition ofclaim 1, characterized by a zeta potential between about −40 mV andabout +40 mV.
 6. The composition of claim 1, characterized by itsability to form a stable aqueous colloidal suspension that exhibits nosubstantial change in hydrodynamic diameter (D_(H)) as determined bydynamic light scattering in 150 mM aqueous NaCl after tangential flowfiltration and storage for one week at room temperature.
 7. Ananoparticle composition comprising: a nanoparticulate metal oxide core,wherein the metal oxide comprises a metal selected from the groupconsisting of iron, tantalum, zirconium, and hafnium; and a shellcomprising a phosphorylated polyol comprising at least two phosphategroups, wherein at least two of the phosphate groups occupy positions inthe phosphorylated polyol which constitute a 1,2 or 1,3 spatialrelationship to one another and the polyol comprises a hydrophilic groupselected from the group consisting of polyethylene ether moieties,polypropylene ether moieties, polybutylene ether moieties, andcombinations of two or more of the foregoing hydrophilic moieties.
 8. Ananoparticle composition, comprising: a nanoparticle metal oxide; and aphosphorylated polyol comprises one or more hydrophilic groups selectedfrom the group consisting of polyethylene ether moieties, polypropyleneether moieties, polybutylene ether moieties, and combinations of two ormore of the foregoing hydrophilic moieties, wherein the phosphorylatedpolyol has structure V

wherein n is an integer from about 16 to about 150 and R¹ is an alkylgroup.